Thrusters operating on hydroxylammonium nitrate (HAN)-based monopropellants are known. See for example “Catalytic Decomposition Of HAN-Water Binary Mixtures,” Courthéoux, et al., 38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Jul. 7-10, 2002 (published by the American Institute of Aeronautics and Astronautics); “Thermal Decomposition Characteristics of HAN Composite Propellant,” Kuwahara et al., the American Institute of Aeronautics and Astronautics, Inc. (1997); and “HAN-based Monopropellant Assessment for Spacecraft,” Robert S. Jankovsky, American Institute of Aeronautics and Astronautics, Inc. (1996), all incorporated herein by this reference.
Typically, a catalyst bed is used to disassociate the monopropellant. See U.S. Pat. No. 4,027,476 incorporated herein by this reference. In U.S. Pat. No. 6,931,832, also incorporated herein by this reference, a rhenium catalyst bed is used behind an aluminum oxide or zirconium oxide porous thermal barrier.
Due to the intense heat generated from using monopropellant fuels, conventional ceramic supported iridium catalysts can degrade. When new non-toxic monopropellants such as HAN or ammonium dinitramide (ADN) based formulations are used, their adiabatic flame temperatures are much higher than that of state of the art monopropellants such as hydrazine. This exacerbates the degradation problem associated with ceramic supported catalysts (either granular or foam types). Moreover, supported catalysts also require bed plates for containment which can be another failure mechanism as the bed plates are in direct contact with the high temperature gas products.
U.S. Pat. No. 4,485,722 discloses iridium, platinum, or ruthenium on an alumina catalyst. In another example, several pieces of expanded titanium sheet clad with platinum foil were used as a catalyst. See also Voecks et al. “Chemical Reactors Based on Catalyzed Wires” incorporated herein by this reference. The concept here was catalyst coated wires (twisted and straight) for a hydrazine monopropellant. Upon information and belief, this concept was never tested or reduced to practice. See also Smith et al. “Kinetics of Hydrazine Decomposition on Iridium and Alumina Supported Iridium Catalysts, Technical final report #AFRPL-TR-73-59, August 1973, distributed by National Technical Information Service, #AD-766 698/5, incorporated herein by this reference.